Ultrasound technology has been used for therapeutic and diagnostic medical procedures, which can include providing imaging of internal portions of a body. Ultrasound procedures typically use a transducer assembly to transmit and/or receive signals. In some cases, a stationary transducer assembly can view a full image area due to the particular positioning or electronic steering of the multiple ultrasound elements in an array. In other designs three-dimensional ultrasound images may be acquired by one-dimensional arrays connected to a mechanical actuator, to move the arrays within the body. Such designs are expensive and can result in a device too large for some vascular or other uses. To achieve good image quality, array transducers must sequentially transmit and receive on many separate channels. That condition requires many expensive and bulky coaxial cables. Fewer coaxial cables can be used, but doing so reduces the quality of the image and image frame rate.
Designs have been proposed including a rotating transducer assembly. Data is obtained by the transducer assembly emitting sequential ultrasound pulses at changing rotational positions. Advantages of the single-element rotational design when compared to an array design include smaller catheter diameter, better image quality, possible higher center frequency, lower cost for the ultrasound imaging console, and less ring down artifacts (dead zone). However, these designs present problems with performing ultrasound procedures in a plane which is parallel to the catheter axis or when performing three-dimensional scans, as it is necessary to rotate the transducer about an axis perpendicular to the catheter axis. Because full 360° rotation in elevation is typically not desirable, reciprocal motion is required.
Single element designs can also include certain disadvantages, such as non-uniform rotational distortion (NURD). During imaging procedures including a single element design, the ultrasound element is typically rotated with a torque cable. Ultrasound pulses are emitted in an even-spaced time-sequential manner under the expectation of a uniform rotation rate of the ultrasound element. Each reflected ultrasound echo signal represents a portion or scan line of an image. An image processor assembles the data based on the assumption that the data points represent images from evenly-spaced pulses. However, it can be difficult to achieve a uniform rotation rate for the ultrasound element when using a torque cable as a driving means. The ultrasound element can be around one meter from the driving end of the torque cable. Ideally, the torque cable will have sufficient stiffness to provide uniform rotation at both ends while simultaneously allowing maneuverability. However, as a practical matter a sufficiently maneuverable torque cable creates a potential for delay in the transferring of torque from one end of the cable to the other, as the cable stores and releases elastic energy, which can cause the transducer assembly to rotate at a non-uniform rate even when the rotation source rotates at a uniform rate. The non-uniform rotation rate causes the resulting images to be distorted.
Thus, there is a need to have an ultrasound system design that could be integrated with a catheter, that is cost effective, small in size, and which produces images free from NURD artifacts and blocked viewing areas.